This invention relates to an improved method and system for monitoring the quality of percussion welds.
The percussion weld process uses electric arc heating and physical impact to join difficult combinations of metals. For example, nominally unweldable silver-cadmium oxide relay contacts are attached to their brass supports by percussion welding. The process is subject to a number of poorly understood variables including changes in part contact resistance, factory line voltage fluctuations, and minute changes in the timing of the weld cycle. It was common for the human operator to judge defective welds based on his experience. Unattended production of consistent, reliable, welded parts requires an automated system which can monitor the process and reject suspect welds. Automatic welding, while potentially highly productive, can result in producing many unacceptable parts because the percussion process drifts. The scrap parts erode automation savings, and marginal welds shorten product life.
Prior attempts at detecting defective welds by analyzing information obtained during the weld event were not entirely successful. Among these are U.S. Pat. No. 3,433,921; the time-varying welding current is sensed and an unacceptable weld is indicated if the maximum current is high during the striking of the arc or falls below a given level just before extinguishment of the arc. U.S. Pat. No. 4,609,806 relates to acoustic monitoring of percussion weld quality and is one of the quality parameters used in the improved monitor of this invention.